Stereotactic ablative radiotherapy (SABR)

Stereotactic ablative radiotherapy (SABR) is a way of giving radiotherapy. It is used to precisely target certain cancers. It’s only suitable for some people, usually those with smaller cancers.

SABR uses small, thin beams of radiation directed from different angles that meet at the tumour. The tumour itself receives a high dose of radiation, while the surrounding healthy tissues receive a low dose. This lowers the risk of damage to normal cells surrounding the tumour.

Planning your treatment is an important part of SABR, and you may need to visit various hospital departments before having the treatment.

The treatment itself is painless. The radiographers won’t be in the same room with you during treatment. They will communicate with you using an intercom and guide you through the process.

Side effects of treatment may include tiredness, skin reactions, soreness and swelling. Side effects may appear just after your treatment and should go away within weeks.

What is stereotactic ablative radiotherapy (SABR)?

Stereotactic ablative radiotherapy (SABR) is a specialised type of radiotherapy. It is sometimes called stereotactic body radiotherapy (SBRT) and may have other names. The names may relate to the area of the body being treated, the type of machinery being used or the length of treatment. They include:

  • extracranial radiosurgery
  • extracranial radiotherapy
  • CyberKnife (a machine used to give SABR).

The most commonly used brand names are CyberKnife, Varian® and Elekta®.

SABR isn’t available in all hospitals in the UK. You may be referred to a specialist hospital if your doctor thinks it’s a suitable treatment for you. In this information we use the term stereotactic ablative radiotherapy, or SABR for short.

How SABR works

Radiotherapy treatment works by damaging the DNA (our genetic material) in cancer cells. The aim is to stop the cancer cells growing and to shrink the tumour or completely destroy it.

Standard radiotherapy delivers a beam of radiation to the treatment area. It’s usually given in a low, daily dose over a period of weeks.

SABR uses many smaller, thin beams of radiation directed from different angles that meet at the tumour. The tumour itself receives a high dose of radiation, while the individual beams that travel through the surrounding healthy tissues are of a low dose. This lowers the risk of damage to normal cells.

SABR can be given with fewer treatments than standard radiotherapy. Treatment will normally be divided into one to eight sessions. The sessions will be spread over a few days and may take up to a couple of weeks to complete. Your doctor will explain how many sessions you need and over how many days (your course of treatment).

There are different machines that can be used to give SABR. Your radiographer will tell you which machine will be used for your treatment. The linear accelerator (linac) that delivers standard radiotherapy can be used to give SABR. There are also specially designed linacs for SABR that are known by their brand names, such as CyberKnife.

The machines work in different ways, so how you prepare for and have your treatment will vary. The radiographer giving your treatment will explain everything to you.

When is SABR used?

SABR can be used to treat small primary lung cancers (cancer that starts in the lung). It can also be used to treat secondary cancers. These are cancers that have spread to another part of the body, for example in the lung, liver, lymph nodes, spine and other sites.

It is also being used to treat prostate cancer in a clinical trial.

SABR may be an alternative to surgery for people who can’t have surgery or where the tumour is in a difficult area to operate on. It is not suitable for everyone. Your doctor can talk to you about whether it’s a treatment option for you.

Planning your SABR treatment

Planning your treatment is an important part of SABR, and you may need to visit different hospital departments before having the treatment.

Radiotherapy staff

There are various members of staff you may meet during the planning and delivery of your treatment. They include:

  • a clinical oncologist, who is a doctor trained in the use of radiotherapy and chemotherapy
  • medical physicists, who are scientists involved in planning how the treatment is given
  • therapeutic radiographers, who are specially trained to operate the machines that give SABR
  • a mould-room technician, who makes masks or moulds for people who need to keep still during treatment
  • nurse and radiographer specialists, who give information and support during your treatment.

Moulds and masks

To help you stay still and in position during the treatment, you may need to have a mould or mask made before planning starts. This is used to help keep you still so that the treatment is accurate and as effective as possible.

Moulds are used to keep a leg or arm, or other body part, still during treatment. Masks keep your head and neck area still during treatment and are often used for treatments to the brain or head and neck area. Sometimes the terms mask and mould are used interchangeably. Sometimes they are called shells or immobilisation devices.

Your doctors will tell you more about this if you need one. We have more detailed information about how radiotherapy masks are made.

Imaging and planning

You will usually start planning by having a CT (computerised tomography) scan (sometimes called a CT simulator). This takes a series of pictures of the area to be treated.

You may also have an MRI scan or a PET scan to improve the accuracy of your treatment.

These scans provide images from different angles to build up a three-dimensional picture of the tumour. Using the information from the scans, a computer is used to make an individual plan for your treatment. This ensures that the radiotherapy is precisely targeted at the tumour and helps to reduce the risk of side effects.

You may have to wait up to two weeks before the plan is ready and you can start treatment.

Metal markers

Your doctor may ask you to have small metal markers placed in or near your tumour. They are sometimes called fiducial markers. The markers help pinpoint the tumour’s exact location and make sure the treatment is given accurately.

The markers are about the size of a grain of rice. They are put in using a needle while you are having a CT or ultrasound scan. You will be given a local anaesthetic injection to numb the skin. You may also be given a mild sedative to make you sleepy. The doctor then makes a small cut and inserts a needle through the skin over the tumour. When the tip of the needle is in the right place, the marker is released. Usually two or three markers are used.

Your doctor will explain the procedure in more detail.

Skin markings

Markings may be made on your skin to help the radiographers position you accurately for the treatment. If you have a mould or mask, some of the marks will be made on this.

Having your SABR treatment

It’s important to tell the hospital staff about any medications and allergies you have. If you take painkillers, you may be advised to take them before your treatment so that you’re comfortable.

The treatment room will be similar to the one you had your planning in. The radiographers won’t be in the room with you when you’re having the treatment, but they will guide you through the process. They will position you carefully on the treatment couch and adjust its height and position. The radiographers will use the marks on your skin (and on your mask, if you have one) to help get you in the same position you were in for your planning scan. It’s important that you’re comfortable, as you have to lie as still as possible during the treatment. Let the radiographers know if you’re not comfortable.

Once you’re in the correct position, the radiographers will leave the room and you’ll be given your treatment. There will be a camera so they can see you from outside the room. Many treatment rooms also have an intercom, so the radiographers can talk to you while you have your treatment. The treatment itself is painless. You may hear a slight buzzing noise from the radiotherapy machine during treatment. Some treatment rooms have CD or MP3 players so you can listen to music to help you relax. If you’d like to listen to your own music, ask your radiographer whether this is possible.

Treatment may be given in one go or it might be broken up with short breaks. Treatment takes between 15 minutes and a couple of hours, depending on the type of machine. Your radiographer will tell you how long your treatment will take.

The way the SABR is given will vary depending on the machine used.

Linac machines have a part called the gantry. This moves around you to give the radiation dose from different angles. The bed you’re positioned on may also be able to move.

CyberKnife machinery has a robotic arm that moves around you, delivering the dose of radiation from different angles.

X-rays and scans may be taken during SABR treatment. This allows for adjustments to be made during each treatment due to tiny changes in the location of the tumour. For example, if the tumour moves slightly as you breathe in and out, the computer can adjust how the treatment is given.

You can usually go home when the treatment is finished.

Possible side effects of SABR

Side effects can be mild or more troublesome depending on the amount of radiotherapy given, the part of the body being treated and the length of the treatment. This information is about the more common, general side effects.

SABR usually causes fewer side effects than standard radiotherapy, as the healthy tissue is exposed to a lower dose of radiation.

The side effects described here won’t affect everyone who has SABR and are usually temporary. Your healthcare team will explain any possible side effects to you before your treatment. It is important to tell your medical team about any side effects you experience.

General side effects

  • Tiredness – you may feel tired for a few weeks after the radiotherapy has been completed.
  • Skin reactions – your skin may become red, dry or itchy about 10–12 days after treatment.
  • Soreness and swelling in the treatment area.

Specific side effects

Some side effects will depend on the area being treated.

Men being treated for a prostate tumour may have urine and bladder problems.

People being treated for a tumour in the spine may develop headaches.

People being treated for a liver tumour may have:

  • sickness (nausea)
  • vomiting
  • pain.

Late side effects

These are side effects that can happen months or years after treatment. They are sometimes called long-term effects, but they are rare. Your doctor or specialist nurse will discuss the likelihood of you developing late side effects.

SABR does not make you radioactive. It is safe for you to be with other people, including children, during and after your treatment.

Your feelings

You may experience many emotions about cancer, including anxiety and fear. These are normal reactions and are part of the process many people go through in trying to come to terms with their condition and its treatments.

Everybody has their own way of coping with difficult situations. Some people find it helps to talk to family or friends, while others prefer to seek help from people outside their situation. Some people prefer to keep their feelings to themselves. There is no right or wrong way to cope, but help is available if you need it.

Back to External beam radiotherapy explained

What is external beam radiotherapy?

External beam radiotherapy is the most common type of radiotherapy. A big machine directs external radiotherapy beams at the affected area.